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- Fabian, Martin, 1960, et al.
(författare)
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PLC-based Implementation of Supervisory Control for Discrete Event Systems
- 1998
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Ingår i: Proceedings of the 37th IEEE Conference on Decision and Control, Tampa, Florida, USA, 16 Dec 1998-18 Dec 1998. ; 3, s. 3305 - 3310
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Konferensbidrag (refereegranskat)abstract
- The supervisory control theory is a general theory for automatic synthesis of controllers (supervisors) for discrete event systems, given a plant model and a specification for the controlled behavior. Though the theory has for over a decade received substantial attention in academia, still very few industrial applications exist. The main reason for this seems to be a discrepancy between the abstract supervisor and its physical implementation. This is specifically noticeable when the implementation is supposed to be based on programmable logic controllers (PLCs), as is the case with many manufacturing systems. The asynchronous event-driven nature of the supervisor is not straightforwardly implemented in the synchronous signal-based PLC. We point out the main problems of supervisor implementation on a PLC, and suggest procedures to alleviate the problems.
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| 4. |
- Hammo, Sari, et al.
(författare)
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Outcome After Endovascular Repair of Ruptured Descending Thoracic Aortic Aneurysm : A National Multicentre Study
- 2019
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Ingår i: European Journal of Vascular and Endovascular Surgery. - : Saunders Elsevier. - 1078-5884 .- 1532-2165. ; 57:6, s. 788-794
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Tidskriftsartikel (refereegranskat)abstract
- Objective: The purpose of this multicentre study was to analyse the outcome of thoracic endovascular aortic repair (TEVAR) in patients with ruptured descending thoracic aortic aneurysm (rDTAA).Methods: This is a nationwide retrospective study including all patients who underwent TEVAR for rDTAA at six major vascular university centres in Sweden between January 2000 and December 2015. Outcome measures were analysed using Kaplan-Meier estimator and multivariable Cox regression.Results: There were 140 patients (age [mean +/- SD] 74.1 +/- 8.8 years; 56% men; aneurysm size 64.8 +/- 19 mm), with rDTAA. In 53 patients (37.9%), the left subclavian artery was covered, and in 25 patients (17.9%) arch vessel revascularisation was performed. In total, 61/136 patients (45%) had a major complication within 30 days post TEVAR. Stroke (n = 20; 14.7%) was the most common complication, followed by paraplegia (n = 13; 9.6%) and major bleeding (n = 13; 9.6%). TEVAR related complications during follow up included endoleaks 22.1% (30/136; 14 type 1a, six type 1b, 10 not defined). In total, re-interventions (n = 31) were required in 27/137 (19.7%) patients. The median follow up time was 17.0 months (range 0-132 months). The Kaplan-Meier estimated survival was 80.0% at one month, 71.7% at three months, 65.3% at one year, 45.9% at three years, and 31.9% at five years. Age (HR 1.03; 95% CI 1.00-1.07; p = .046), history of stroke (HR 2.35; 95% CI 1.194.63; p = .014), previous aortic surgery (HR 2.11; 95% CI 1.15-3.87; p = .016) as well as post-operative major bleeding (HR 4.40; 95% CI 2.20-8.81; p = .001), stroke (HR 2.63; 95% CI 1.37-5.03; p = .004), and renal failure (HR 8.25; 95% CI 2.69-25.35; p = .001) were all associated with mortality.Conclusions: This nationwide multicentre study of patients with rDTAA undergoing TEVAR showed acceptable short- but poor long-term survival. Adequate proximal and distal aortic sealing zones are important for technical success. High risk patients and post-operative complications need to be further addressed in an effort to improve outcome.
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- Hellgren, Anders, 1970, et al.
(författare)
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Database Design for Machining Cell Resource Models
- 1998
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Ingår i: Preprints of the 8th IFAC/IFORS/IMACS/IFIP Symposium on Large Scale Systems: Theory and Applications, Rio-Patras, Greece.
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Konferensbidrag (refereegranskat)
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| 6. |
- Hellgren, Anders, 1970, et al.
(författare)
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Deadlock Detection and Controller Synthesis for Production Systems Using Partial Order Techniques
- 1999
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Ingår i: Proceedings of the 1999 IEEE International Conference on Control Applications, Kohala Coast, Hawaii, USA.
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Konferensbidrag (refereegranskat)abstract
- Discrete event systems can be used to model the behaviour of production systems. The supervisory control theory is a suitable tool for synthesising controllers that coordinate the resource utilisation of concurrent products in the production system. Due to the combinatorial state space explosion, computations become intractable for most real life systems. To alleviate this problem, methods that do not enumerate the entire state space are needed. One method that has proven valuable for the verification of concurrent systems is based on partial order principles. For a certain class of production systems it is shown how such ideas may be used to synthesise non-blocking discrete event controllers.
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| 8. |
- Hellgren, Anders, 1970, et al.
(författare)
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Modelling and PLC-based Implementation of Modular Supervisory Control
- 2002
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Ingår i: Proceedings of the 6th Workshop on Discrete Event Systems, Zaragoza, Spain, OCT 02-04, 2002. ; , s. 371-376
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Konferensbidrag (refereegranskat)abstract
- Implementation of supervisory control in Programmable Logic Controllers (PLCs) typically requires that the underlying discrete event models of plant, specification as well as the supervisor itself fulfil a number of properties. These properties are discussed and methods for solving related problems are given. In particular, determinism and synchronisation issues are investigated.In a manufacturing system, for instance, there are typically a set of processes using a set of shared resources. Uncareful modelling may cause the system model to become nondeterministic. This can be circumvented by relabelling the relevant models. For industrial-sized models, though, this must be done automatically, something that we achieve by parameterising the models.Given a deterministic model, consisting of several interacting entities, we discuss its PLC-based implementation. In addition to the synchronisation of plant and supervisor, a modular supervisor must be internally synchronised. However, synchronisation of the submodules is not well defined in the PLC-world. This may be achieved by using event monitors and an immediate transit/immediate action execution model.
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| 9. |
- Hellgren, Anders, 1970, et al.
(författare)
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Modular Implementation of Discrete Event Systems as Sequential Function Charts Applied to an Assembly Cell
- 2001
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Ingår i: Proceedings of the 2001 IEEE Conference on Control Applications, SEP 05-07, 2001 Mexico City, Mexico. - 0780367332 ; , s. 453-458
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Konferensbidrag (refereegranskat)abstract
- Modular implementation of discrete event models in Programmable Logic Controllers (PLCs) using Sequential Function Charts (SFCs) is investigated. Synchronisation of such models, typically finite state automata of Petri nets, is not well defined in the synchronous PLC-world. We develop an algorithm that computes event monitors for synchronising concurrently executing SFCs. The methodology is applied to an assembly cell.
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